The present invention relates to a mechanical device for simplifying fluid balance in a filtration system, particularly a continuous arterio-venous hemofiltration (CAVH) system. Continuous arteriovenous hemofiltration (CAVH) has become a valuable tool in the treatment of acute renal failure in critically ill patients.
In patients experiencing acute or chronic renal failure, the elimination of excess water and waste products is conventionally performed by hemodialysis. This mode of treatment is quite different from the function of natural kidneys. Hemodialysis utilizes relatively high cost, technically sophisticated, electronically controlled machines to effect this process. Connections to electricity and to pure water (deionized water or reverse osmosis water) are necessary. Moreover, association with a regular technical service is required and the procedure must be performed by specialized nurses and physicians. A standard hemodialysis treatment regimen is 3X5 hours during one week. As excess water and waste products are eliminated quite rapidly during the short treatment periods, hemodynamic instability is a common side effect. The same is generally true for mechanical hemofiltration, although there are differences in quantity.
A recently developed mode of treating patients who have acute renal failure is with continuous arterio-venous hemofiltration This treatment is directed primarily to patients who are immobilized and must be treated using a mechanical respiratory assist. By the use of this mode of treatment, some of the disadvantages of conventional therapy can be eliminated and the attendant costs reduced.
In continuous arterio-venous hemofiltration, a small capillary hemofilter is connected to both a patient's artery and vein to provide access to the patient's blood. The filter capillaries are permeable to water and non-protein bound substances up to a molecular weight of 10000 to 50000 daltons. Blood cells and protein, however, remain within the blood compartment. This treatment is intended to simulate the function of the patient's kidneys. Filtration is driven by the patients circulation without the necessity for an extracorporeal pump. Only 1 to 2% of the patient's circulation is used for this extracorporeal circulation. As the pressure gradient between the arterial and venous blood vessels is the driving force, the procedure was named continuous arteriovenous hemofiltration (CAVH). After filtration, filtrate generated is discarded and a substitute is infused into the venous line. Every hour a volume of between 500 and 1000 ml has to be manually balanced by a nurse. Manual handling of a daily fluid exchange of between 12 and 20 liters presents certain problems in patient care due to a possible imbalance.